Drugs that interact with oral contraceptives
Drugs which increase the metabolism of oestrogens and progestogens can reduce the efficacy of oral contraceptives.
This occurs when the drugs induce the activity of metabolising enzymes in the liver and intestinal mucosa. One example is the complementary medicine St John's wort which can potentially lead to a failure of oral contraception.
Although not an enzyme inducer, griseofulvin can also potentially reduce the efficacy of hormonal contraceptives.
Drugs which can reduce the effectiveness of oral contraceptives include:
- St John’s wort
Note: Guidelines published in the UK and USA no longer recommend additional contraceptive